Asynchronous motor with features creating magnetic field disturbance

Abstract

A component for introducing disturbances into the magnetic field of an asynchronous motor by altering a reluctance of the motor is disclosed. An asynchronous motor is provided that includes a stator having a plurality of windings that is configured to generate a rotating magnetic field when a current is provided to the plurality of windings. The asynchronous motor also includes a rotor positioned within the stator configured to rotate relative thereto responsive to the rotating magnetic field and a component separate from the stator and the rotor that is positioned within the rotating magnetic field, with the component being configured to alter a magnetic reluctance of the rotor so as create a disturbance in the rotating magnetic field.

What is claimed is: 
     
       1. An asynchronous motor comprising:
 a stator including a plurality of windings and being configured to generate a rotating magnetic field when a current is provided to the plurality of windings; 
 a rotor positioned within the stator and configured to rotate relative thereto responsive to the rotating magnetic field; 
 a component separate from the stator and the rotor and positioned within the rotating magnetic field, the component being configured to alter a magnetic reluctance of the rotor so as create a disturbance in the rotating magnetic field; and 
 a motor drive to control current and voltage provided to the stator, the motor drive including a processor programmed to:
 measure a stator phase voltage spectrum of the stator; 
 apply a fast Fourier transform to the stator phase voltage spectrum to translate the stator phase voltage spectrum from a time domain to a frequency domain; 
 determine a speed of the rotor based on an applied stator frequency in the stator phase voltage spectrum and a stator phase voltage spectrum peak. 
 
 
     
     
       2. The asynchronous motor of  claim 1  wherein the component comprises a ferrous component having ferromagnetic properties. 
     
     
       3. The asynchronous motor of  claim 1  wherein the rotor comprises:
 a rotor core; and 
 a squirrel cage rotor mechanically coupled to the rotor core and positioned thereabout; 
 wherein the component is mechanically coupled to the rotor core and positioned adjacent to one end of the squirrel cage. 
 
     
     
       4. The asynchronous motor of  claim 1  further comprising a motor drive to control current and voltage provided to the stator, the motor drive including a processor programmed to:
 measure a stator phase current spectrum of the stator; 
 apply a fast Fourier transform to the stator phase current spectrum to translate the stator phase current spectrum from a time domain to a frequency domain; 
 determine a speed of the rotor based on observed frequencies within the stator phase current spectrum. 
 
     
     
       5. The asynchronous motor of  claim 4  wherein the processor is further programmed to determine the speed of the rotor based on an applied stator frequency in the stator phase current spectrum and a stator phase current spectrum peak. 
     
     
       6. The asynchronous motor of  claim 5  wherein the disturbance in the rotating magnetic field created by the component introduces a stator current spectral component into the stator phase current spectrum, with the stator current spectral component introduced by the component comprising the stator phase current spectrum peak used to determine the speed of the rotor. 
     
     
       7. The asynchronous motor of  claim 6  wherein the processor is further programmed to introduce at least one of a variable load and a variable eccentricity to the asynchronous motor to introduce a stator current spectral component into the stator phase current spectrum, with the stator current spectral component introduced into the stator phase current spectrum by the at least one of the variable load and the variable eccentricity being at a same frequency as the stator current spectral component introduced by the component. 
     
     
       8. The asynchronous motor of  claim 7  wherein the processor is further programmed to combine the stator current spectral component introduced from the at least one of the variable load and the variable eccentricity with the stator current spectral component introduced by the component to form a combined stator current spectral component having an increased amplitude. 
     
     
       9. The asynchronous motor of  claim 1  comprising one of a single phase motor and a multi-phase motor. 
     
     
       10. The asynchronous motor of  claim 1  wherein the component comprises:
 a body; and 
 a plurality of projections extending out from the body, the plurality of projections being spaced apart such that a plurality of slots are formed between the plurality of projections. 
 
     
     
       11. An asynchronous motor comprising:
 a stator including a plurality of windings and being configured to generate a rotating magnetic field when a current is provided to the plurality of windings; 
 a rotor positioned within the stator and configured to rotate relative thereto responsive to the rotating magnetic field; and 
 a component separate from the stator and the rotor and positioned within the rotating magnetic field, the component being configured to alter a magnetic reluctance of the rotor so as create a disturbance in the rotating magnetic field; 
 wherein the component comprises:
 a body; and 
 a plurality of projections extending out from the body, the plurality of projections being spaced apart such that a plurality of slots are formed between the plurality of projections. 
 
 
     
     
       12. An asynchronous motor comprising:
 a stator including a plurality of windings and being configured to generate a rotating magnetic field when a current is provided to the plurality of windings; 
 a rotor positioned within the stator and configured to rotate relative thereto responsive to the rotating magnetic field; 
 a component separate from the stator and the rotor and positioned within the rotating magnetic field, the component being configured to alter a magnetic reluctance of the rotor so as create a disturbance in the rotating magnetic field; and 
 a motor drive to control current and voltage provided to the stator, the motor drive including a processor programmed to:
 measure a stator phase current spectrum of the stator; 
 apply a fast Fourier transform to the stator phase current spectrum to translate the stator phase current spectrum from a time domain to a frequency domain; and 
 determine a speed of the rotor based on observed frequencies within the stator phase current spectrum, with the determination being based on an applied stator frequency in the stator phase current spectrum and a stator phase current spectrum peak; 
 
 wherein the disturbance in the rotating magnetic field created by the component introduces a stator current spectral component into the stator phase current spectrum, with the stator current spectral component introduced by the component comprising the stator phase current spectrum peak used to determine the speed of the rotor; and 
 wherein the processor is further programmed to introduce at least one of a variable load and a variable eccentricity to the asynchronous motor to introduce a stator current spectral component into the stator phase current spectrum, with the stator current spectral component introduced into the stator phase current spectrum by the at least one of the variable load and the variable eccentricity being at a same frequency as the stator current spectral component introduced by the component. 
 
     
     
       13. An asynchronous motor comprising:
 a stator including a plurality of windings and being configured to generate a rotating magnetic field when a current is provided to the plurality of windings; 
 a rotor positioned within the stator and including a rotor core and a plurality of rotor bar conductors, the rotor configured to rotate relative to the stator responsive to the rotating magnetic field; 
 a component positioned adjacent to the rotor and configured to alter a reluctance of the asynchronous motor so as to generate a disturbance in the rotating magnetic field, wherein the disturbance in the rotating magnetic field generated by the component introduces a current signal into a stator phase current spectrum of the stator; and 
 a motor drive to control current and voltage provided to the stator, the motor drive including a processor programmed to:
 measure the stator phase current spectrum of the stator; 
 apply a fast Fourier transform to the stator phase current spectrum to translate the stator phase current spectrum from a time domain to a frequency domain; and 
 determine a speed of the rotor based on an applied stator frequency in the stator phase current spectrum and a stator phase current spectrum peak, the stator phase current spectrum peak corresponding to the current signal introduced by the component; 
 
 wherein the processor is further programmed to vary at least one of a load and an eccentricity of the asynchronous motor to introduce a current signal into the stator phase current spectrum to increase an amplitude of the stator current spectral component introduced by the component. 
 
     
     
       14. The asynchronous motor of  claim 13  wherein the component is formed of a ferromagnetic material or a paramagnetic material. 
     
     
       15. The asynchronous motor of  claim 13  wherein the component is mechanically coupled to the rotor core or a rotor shaft extending out from the rotor core and is positioned within the rotating magnetic field generated by the stator. 
     
     
       16. An x-ray tube comprising:
 a housing enclosing a vacuum chamber; 
 a cathode positioned within the vacuum chamber and configured to emit electrons; 
 an anode positioned within the vacuum chamber to receive the electrons emitted from the cathode and configured to generate a beam of x-rays from the electrons; and 
 an induction motor configured to rotate the anode, the induction motor comprising:
 a stator including a plurality of windings and being configured to generate a rotating magnetic field when a current is provided to the plurality of windings; 
 a rotor positioned within the stator and configured to rotate relative thereto responsive to the rotating magnetic field, thereby causing the anode to rotate; and 
 a component positioned on one end of the rotor and being configured to alter a reluctance of the rotor, thereby creating a disturbance in the rotating magnetic field, and 
 
 a motor drive to control current and voltage provided to the induction motor, the motor drive including a processor programmed to:
 measure a stator phase current spectrum of the stator; 
 apply a fast Fourier transform to the stator phase current spectrum to translate the stator phase current spectrum from a time domain to a frequency domain; and 
 determine a speed of the rotor based on observed frequencies within the stator phase current spectrum; 
 
 wherein the component is configured to create a disturbance in the rotating magnetic field so as to introduce a stator current spectral component in the stator phase current spectrum that is detectable by the processor, such that the stator current spectral component provides for the determination of the speed of the rotor; and 
 wherein the processor is further programmed to vary at least one of a load and an eccentricity of the asynchronous motor to introduce a stator current spectral component into the stator phase current spectrum, with the stator current spectral component introduced by the variation of the at least one of the load and the eccentricity increasing an amplitude of the stator current spectral component introduced by the component. 
 
     
     
       17. The x-ray tube of  claim 16  wherein the housing includes a rotor can positioned about the rotor such that the rotor is within the vacuum chamber, the stator being positioned about the rotor outside of the rotor can and outside the vacuum chamber, and wherein the component is positioned adjacent the rotor inside the vacuum chamber. 
     
     
       18. The x-ray tube of  claim 16  wherein the component comprises a ferrous component having ferromagnetic properties.